Watch the Dominant Soloing 2: 16 online guitar lesson by Brad Carlton from Bluesology 1

Living inside our major scales are the major and minor pentatonic scales we so fondly use in our day to day musical adventures. They are five tone subsets of our seven tone diatonic scales. For the I, IV, and V chords, all of which are major chords in the major scale; there is a corresponding major pentatonic scale. Likewise, the ii, iii, and vi minor chords also have their corresponding minor pentatonic scales.
Pay attention, this is an enlightening lesson.